A hard disc drive system utilizes a mechanism for magnetically recording and retrieving information that includes a head and a spinning disc coated with a thin, high-coercivity magnetic material called the media. Reliable operation of the mechanism is acutely sensitive to the spacing between the head and the media. Many technologies address the control of this spacing. In particular, various mechanisms are used to provide more reliable operations for writing data to the media and reading data from the media.
Information is written to the media by manipulating the magnetization direction of volume elements in the media surface. The magnetization direction in the media is changed by a switching field caused by a writer over the media surface. The electromagnet is fabricated on a substrate. A slider can include the substrate and the writer. Magnetic flux supplied by the electromagnet is sufficiently strong to change the direction of magnetization, or write information, in the high-coercivity media.
It is desirable to have the flux tightly localized so that alteration of magnetization direction occurs only in the intended volume element, and not in adjacent elements. The degree of localization of the flux used to write to the media depends strongly on the separation of the writer from the surface of the media. Primary control of writer to media separation is done using a stiff air bearing formed by the interaction of laminar air flow caused by the spinning disc and air bearing structures on an air bearing surface of the slider.
Information is read from the media using a sensor, or reader, over the media surface. The slider can include the reader. The reader detects the direction of magnetization and provides a signal indicative thereof. The strength of the sensed direction of magnetization also largely depends on the separation between the reader and the media surface, and the ability to read an isolated region of specific magnetization (i.e. a “bit” of data) also depends on the separation between the reader and the media surface.
As product performance requirements have risen, requirements for head media spacing control have tightened. A secondary separation control is typically employed to meet these requirements. One control includes electrically heating the head, which causes thermal expansion of the head and modifies the head media spacing. The heated region protrudes from the air bearing surface, reducing the head media spacing. The shape of the protrusion can be concentrated proximate the writer, with minimal protrusion elsewhere in order to minimize adverse effects caused by other portions of the air bearing surface from getting too close to the media. Only providing a heater proximate the writer does not allow precise separation control between the reader and the media surface.
Additionally, only providing a heater proximate the writer can create problems when calibrating control of the heater to provide a desired head media spacing. An electronic control system used to control the heater power can be calibrated on a head by head basis. The calibration requires heating the writer to reduce head disc separation to such an extent that the protruded region of the head contacts a lubricant layer on the media. Additional drag from the lubricant layer on the head causes a detectable increase in an error correction signal generated by a positioning system that is used to position the head at a position over the media. Once contact between the head and lubricant layer is detected, the heater setting can be adjusted (for example reduced) to ensure a minimal separation between the writer and the media for reliable operation that does not cause damage to the head and/or media.
However, requirements for detecting contact and writing to the media are different. For detecting contact, a larger area is desirable. A larger protrusion area can interact strongly with the lubricant layer and create an easily detectable error signal. On the other hand, a highly localized protrusion region proximate the writer will create a more reliable write operation. Furthermore, contact detection with a small protrusion region can create difficulty when detecting contact with the media, which can result in damage to the head and/or the media. Because protrusion of any specific area (for instance a writer pole) from an air bearing surface to near contact with the media will leave other areas (for instance a reader) further from the media, protruding a single area may offer inadequate control over spacing between other areas. In this context, head spacing or protrusion requirements for reading and writing are also different.
Electrical contacts on a slider body are limited. Contacts on the slider have physical size limitations due to manufacturing processes and limited slider dimensions. Additional contacts and increased line count may deleteriously impact suspension cost as well as decrease mechanical and electrical performance. Use of a single contact to control multiple actuators would allow reduction of contact pads and leads connecting to the slider.